The UN body for enforcing international drug treaties, the International Narcotics Control Board (INCB), voiced concern over "misguided initiatives" on cannabis legalisation in Uruguay and the American states of Colorado and Washington, which failed to comply with international drug conventions.

The INCB annual report published this week claimed that the introduction of a widely commercialised "medical" cannabis programme in Colorado had led to increases in car accidents involving "drug drivers", cannabis-related treatment admissions, and positive drug tests for cannabis.

"Drug traffickers will choose the path of least resistance, so it is essential that global efforts to tackle the drug problem are unified," said INCB president Raymond Yans.

He added that the UN was concerned about initiatives for the legalisation of the nonmedical and nonscientific use of cannabis, which posed "a very grave danger to public health and well-being" – what international drug conventions had been designed to protect.

The UN's warning followed the vote by Uruguay's Parliament in December, to approve a Bill to legalise and regulate the sale and production of cannabis.

The sale of cannabis by licensed suppliers to adults over 21 became legal in Colorado in January, with Washington state due to follow. This was despite it remaining illegal – under United States federal law – to cultivate, sell or possess cannabis.

Uruguay President José Mujica said his country’s move was a bid to undermine the black market, and find alternatives to the "war on drugs".

But the INCB report argued against such "alternative drug regimes", claiming legalisation would not collapse "underground markets" – it would lead to greater use of such drugs and higher levels of addiction.

Citing alcohol and tobacco markets, the report said, despite legalisation, there was still a thriving black market in many countries.
It said up to 20% of Britain's domestic cigarette market consisted of smuggled cigarettes, and they represented 33% of all domestic cigarette consumption in Canada. Alcohol, despite being legal, was also responsible for far more arrests than illegal drugs. In the US there were two million alcohol-related arrests in 2012 compared with 1.6-million related to illegal drugs.

"One reason for the higher alcohol-related costs is that in many countries alcohol abuse is far more prevalent than the abuse of substances under international control," the report stated.

Ann Fordham, of the International Drug Policy Consortium, said: "While the board’s interest in ensuring access to medicines for the relief of pain and suffering is positive, it remains in denial of the urgent calls to have a meaningful debate on the future of global drug policy. The board is apparently oblivious to the growing number of member states questioning the status quo and exploring alternative policies."